The present invention relates to a method for producing a solar battery having semiconductor film on insulating substrate, particularly to a method for producing an integrated solar battery produced using laser beam processing.
In recent years, a thin film solar battery in which non-monocrystal silicon film is formed on an insulating substrate is getting attention. Here, the substance applied as non-monocrystal silicon is amorphous silicon, microcrystal silicon, thin film polycrystal silicon, and compound thereof. A thin film solar battery is characterized in that production cost is kept low and material used for production is little. By using plastic film substrate having flexibility as an insulation substrate, shape of the solar battery is set freely. It is one of important characteristics to make an integrated structure possible on the insulation substrate, where desired voltage is obtained by dividing an element to plural elements on single substrate and connecting the elements in series. It is possible to use a substrate having an insulating surface, for example a conductive substrate on which an insulating film is provided.
Laser beam process is used widely for producing a solar battery of integrated structure. The laser beam process irradiates laser beam gathered on a certain area to a work piece, makes a hole by melting, evaporation, or scattering, performs melting, cutting off, and marking, and divides, thereby any shape can be processed by scanning laser beam. By this technique, separation of thin film can be performed with scribing width of equivalent width in high speed. The laser beam process is used even for means melting and connecting taking-out electrodes of the solar battery. Although the process is called bonding especially, the process is included in the laser beam process.
There has been technique of photolithography hitherto as a method for shape-processing pattern for the purpose of electrode and semiconductor layer constituting solar battery. Patterning process of the solar battery using the photolithography applies a resist to allover face of the work piece, exposes through a mask, and after that, a resist mask is formed at developing process. Next, area except masked area with the resist is etched by etching process, after that, the resist is peeled off by alkali solvent, and cleaning and drying are performed, thereby the process is completed. The process has problems of complexity and many process steps, long processing time, and high production cost.
The patterning process of the solar battery by laser beam process is simple and few in number of processes. It has a distinguishing characteristic that the processes are completed only by irradiating laser beam while scanning at a part desired to perform patterning.
The laser beam process irradiates laser beam, melts a part of work instantly, and evaporates or scatters. At this time, material of the part of work melted at high temperature is cooled while scattering or after sticking at periphery, and becomes particles of powder condition. The particles of powder condition damage generating layer of the solar battery at manufacturing process after the laser beam process, thereby causes one of decline in characteristic.
Here, producing process of the solar battery using laser beam process of the prior art will be described using FIGS. 2A to 2E. First, a lower electrode 202 is formed on a substrate 201, and on the lower electrode 202, a semiconductor layer 203 being a generating of the solar battery is formed as shown in FIG. 2A. Next, to make an integrated structure of the solar battery on the same substrate, the lower electrode layer and the semiconductor layer are divided by laser beam process, and plural sections are made. Divided parts 204a and 204b by laser beam process are shown in FIG. 2B. At the laser beam process, the semiconductor layer and the lower electrode of the divided portions are melted and scattered by the laser beam. Particles 205a, 205b, and 205c of powder condition generated at this time scatter and stick on the semiconductor layer 203 of periphery. The particles possibly get stuck in the semiconductor layer 203.
After the laser beam process, insulating layers 206a and 206b are formed. This is because contact of the lower electrode and an upper electrode is prevented when the conductive upper electrode is formed on the divided portion. The state using thermosetting resin as insulating layer and forming with screen printing method is shown in FIG. 2C. Insulating thermosetting resin 208 is applied on a screen printing plate 207, a squeegee 209 is moved to direction 210 from right to left of the figure, and resin is printed at parts of the insulation layers 206a and 206b. At the printing, the screen-printing plate 207 contacts the semiconductor layer 203 and particles of powder condition, and presses the particles of powder condition against the semiconductor layer. Even the particles of powder condition stuck on surface of the semiconductor layer are possibly taken in the semiconductor layer.
In the printing process, when the screen-printing plate is separated from the semiconductor layer and further after the printing process, particles of powder condition possibly desorbs from surface of semiconductor layer or inside. Parts 212a, 212b, and 212c where the particles of powder condition are desorbed exist at the semiconductor layer as shown in FIG. 2D.
Although the upper electrodes 213a, 213b, and 213c are formed as shown in FIG. 2E after the printing process and drying process, at this time, parts 215b and 215c where the upper electrode and the lower electrode contact are formed at parts 212b and 212c where the lower electrodes expose among the desorbed parts 212a, 212b, and 212c. Since the upper electrode and the lower electrode contact at unit cells 214b and 214c, characteristic of the solar battery such as release voltage decreases. At a part 212a where the lower electrode is not exposed, a part 215a where the upper electrode and the lower electrode are close is formed. Although characteristic of the solar battery such as release voltage does not decrease directly by cause of the close part 215a, damage caused by static electricity occurs easily at dealing as a product.
Although method forming insulation layer using screen printing method is described in FIGS. 2A to 2E, in the case forming insulation layer by another method or using another producing process of the solar battery, generation of the particles of powder condition can not be avoided as long as the laser beam process is performed. Although particles of powder condition generated at laser beam process stick at semiconductor layer and get in inside of the layer, the particles drop out by process forming the upper electrode, and the upper electrode contacts the lower electrode at forming the upper electrode.
As one means to reduce foreign bodies of fine particles, there is a method adjusting condition of laser power, that is, feeding speed of a part of work in laser beam processing device. For example, means making laser power weak, that is, making feeding speed of the working portion fast may be used. However, particles of powder condition generated at laser beam process can reduce using the means, however, it is impossible to remove the entire particles. For example, although it is possible to make the sizes small or to reduce numbers of particles of powder condition 205a, 205b, and 205c shown in FIG. 2B, it is impossible to remove the entire particles.
As another means to reduce foreign bodies of fine particles, a method absorbing particles of power condition generated at process in laser beam processing device using absorbing mechanism. However, although material of a part processed by laser melts and scatters instantly, scattering speed is considerably high and temperature is high. Because of that, removing the particles of powder condition before adhesion to generating layer of the solar battery or removing the particles of powder condition stuck is not performed completely even by using strong absorbing mechanism.
The invention is performed in view of the above-mentioned problem, an object of the invention is to prevent decrease of characteristic of the solar battery and production yield caused by particles of powder condition generating from a part of work at laser beam process.